<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title>Titie</title>
		<meta name="viewport" content="width=device-width,initial-scale=1, shrink-to-fit=no">
		<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.1.3/dist/css/bootstrap.min.css" rel="stylesheet">
		<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.1.3/dist/js/bootstrap.bundle.min.js"></script>
		<style>
			div {
				width: 200px;
				height: 50px;
			}
		</style>
	</head>
	<body class="container">
		<h3 class="border border-primary mb-4 mx-auto" style="width: 150px;">mx-auto</h3>
		<div class="border border-primary ml-4">mb-4</div>
		<div class="border border-primary">正常</div>
		<div class="border border-primary ml-n4">ml-n4</div>
	</body>
</html>
